Fix compilation of patterns incorporating ECLASS and lookbehinds

[NWilson]

Reported in #959

[carenas]

I had the following tests instead in my version, which are IMHO more realistic and cover also the perl class syntax:

diff --git a/testdata/testinput1 b/testdata/testinput1
index 64b697f3..91e2c7a1 100644
--- a/testdata/testinput1
+++ b/testdata/testinput1
@@ -7154,6 +7154,13 @@ $/x
 \= Expect no match
     z
 
+/(?[\d-[1]]).(?<!x)/
+    0a
+    90
+\= Expect no match
+    1a
+    0x
+
 /^.{4}/s
     abcdef
     abcde
diff --git a/testdata/testinput2 b/testdata/testinput2
index a7c1c846..c205e68e 100644
--- a/testdata/testinput2
+++ b/testdata/testinput2
@@ -7407,6 +7407,13 @@ a)"xI
 /[^[[^]~~[^]]]/B,alt_extended_class,allow_empty_class
     a
 
+/[\d--1].(?<!x)/alt_extended_class
+    0a
+    90
+\= Expect no match
+    1a
+    0x
+
 # --------------
 

[NWilson]

Thanks @carenas! That's a good testcase, I've added it to my PR.

[carenas]

the Perl compatible extended class syntax test could have gone to test1 as was originally suggested, though

[NWilson]

Most of the perl eclass tests are in testinput2. I put it with the existing block.